1. Field of the Invention
The present invention relates to a cleaning blade and an image forming apparatus.
2. Description of the Related Art
An image forming apparatus employing an electrophotographic system (occasionally simply referred to as the “image forming apparatus” hereinafter) is used for various purposes in many industrial fields, because the image forming apparatus is capable of forming a high-quality image with a simple operation and a maintenance checkup thereof is simple. The image forming apparatus comprises, for example, a photoreceptor drum, a charging section, an exposure section, a developing section, a transfer section, a fixing section, and a cleaning section. The photoreceptor drum has a photosensitive layer on the surface thereof. The charging section charges the surface of the photoreceptor drum. The exposure section irradiates the surface of the photoreceptor drum having been charged with a signal light, thereby forming an electrostatic latent image. The developing section supplies toner to the electrostatic latent image to form a toner image. The transfer section transfers the toner image to a recording medium. The fixing section fixes the toner image to the recording medium by heating and pressurizing. The cleaning section includes a cleaning blade that is disposed so as to abut on the surface of the photoreceptor drum, and removes extra toner, paper dust and so on adhering to the surface of the photoreceptor drum.
Although the image forming apparatus is capable of forming a high-quality image as described above, the image forming apparatus is expected to have a higher performance in accordance with the wide spread thereof. For example, reduction of consumed electric power is required. For the reduction of consumed electric power, it is chiefly considered to decrease a heating temperature (occasionally referred to as the “fixing temperature” hereinafter) at the time of fixing of the toner image to the recording medium. As one part thereof, toner is provided with low-temperature fixability by increase of the content of a release agent (wax) in the toner. However, the release agent has a weak point of not remaining in toner particles but seeping out to the surface of the toner. Therefore, in a case where the toner remains on the surface of the photoreceptor drum after the toner image is transferred to the recording medium, the release agent seeps out from the inside of the remaining toner and adheres to the surface of the photoreceptor drum. Then, the release agent is spread by the cleaning blade in a relatively wide range in the circumferential direction of the photoreceptor drum, whereby such a phenomenon called filming tends to occur very easily that the release agent adheres like a film to the surface of the photoreceptor drum. The filming hinders uniform charge of the surface of the photoreceptor drum, resulting in occurrence of an image failure such as an image blur that impairs clearness of the image. Moreover, the toner may adhere or fuse onto the cleaning blade, thereby causing an image failure such as a white line. Accordingly, a technique of decreasing the fixing temperature by using toner with low-temperature fixability has problems to be solved, such as prevention of occurrence of the filming and prevention of adhesion or fusion of the toner.
For these problems, a technique of preventing the release agent from being spread, by decreasing the surface energy of the photoreceptor drum and/or the cleaning blade has been proposed in various patterns. For example, a technique of applying a lubricating agent to the surface of the photoreceptor drum is proposed. In this technique, a mechanism for applying the lubricating agent to the surface of the photoreceptor drum needs to be disposed inside the image forming apparatus, because the lubricating agent is a consumable item. Addition of such a mechanism makes the image forming apparatus large in size and makes the internal structure of the image forming apparatus complicated, lowers simplicity of the maintenance checkup, the service life, convenience, and so on, of the image forming apparatus, and raises the cost of manufacture thereof. Further, a technique of making the photosensitive layer on the surface of the photoreceptor drum contain fluorine resin particulate is proposed. In a case where the photosensitive layer is made to contain the fluorine resin particulate, there is the fear that the sensitivity to the signal light irradiated by the exposure section deteriorates and image reproducibility is impaired. Moreover, there is the fear that pinholes due to the fluorine resin particulate are generated in the photosensitive layer, uniform chargeability of the photosensitive layer is impaired, and an image failure is caused. Further, a technique of providing a fluorine resin layer on the surface of the cleaning blade is proposed. Since this fluorine resin layer gradually abrades away as being rubbed against the photoreceptor drum, the fluorine resin layer will not exert a sufficient effect all through the service life of the photoreceptor drum.
Furthermore, in Japanese Unexamined Patent Publication JP-A 2003-195711, such a cleaning blade is proposed that is composed of a material obtained by dispersing 0.1 part by mass through 50 parts by mass of resin particulate made of vinyl resin, fluorine resin or polyester and having a number average particle diameter of 0.01 μm through 30 μm, into 100 parts by mass of polyurethane rubber. In JP-A 2003-195711, there is a specific description on the effect of the fluorine resin particulate, only for fluorine resin particulate that is a copolymer of ethyl fluoride methacrylate, methyl methacrylate and styrene produced in example 5 of production of the resin particulate described in paragraph [0104]. Moreover, JP-A 2003-195711 describes that 0.1 part by mass through 50 parts by mass of the resin particulate is added to 100 parts by mass of polyurethane rubber of the base material, but the addition amount of the fluorine resin particulate specifically disclosed in table 1 of paragraph [0124] is merely 5 parts by mass. Since the fluorine resin particulate described above does not have sufficient wettability on polyurethane rubber of the base material, uniform dispersiveness in the base material is impaired when 15 parts by mass or more of the fluorine resin particulate is added to 100 parts by mass of the base material. As a result, the mechanical strength, and further, service life of the entire cleaning blade may decrease. In paragraph [0042], polytetrafluoroethylene is also described as the fluorine resin. However, even if the polytetrafluoroethylene particulate is used by 5 parts by mass, which is the addition amount of the fluorine resin particulate specifically disclosed in paragraph [0124], occurrence of a cleaning failure at a relatively small number of printed sheets cannot be avoided. Moreover, JP-A 2003-195711 does not disclose anything about use of the cleaning blade disclosed therein in the image forming apparatus using the toner in which the content of the release agent is increased in order to enhance low-temperature fixability.
Furthermore, in Japanese Unexamined Patent Publication JP-A 2006-91566, a cleaning blade including a base and a skin layer is proposed. In the technique of JP-A 2006-91566, the base is a hardened body of polyurethane composition, which has an average particle diameter of 0.1 mm through 0.5 mm and which contains low-hardness particulate having lower hardness than the skin layer. The skin layer is a layer that is disposed to at least the surface of the base at a portion rubbed against the surface of the photoreceptor drum and that does not contain the low-hardness particulate. Moreover, claim 2 of JP-A 2006-91566 describes that the low-hardness particulate is composed of one kind or two kinds or more selected from among urethane elastomer, polyester elastomer, fluorine rubber, silicone rubber, and cellulosic polymer. The low-hardness particulate composed of fluorine rubber specifically used in an example is an ethylene tetrafluoroethylene copolymer having an average particle diameter of 0.5 mm (product name: Fluon CD086 produced by Asahi Glass Co., Ltd.). However, in a case where the skin layer is provided at the rubbed portion of the surface of the base, the skin layer gradually abrades away by being rubbed against the surface of the photoreceptor drum, and an effect of the skin layer of reducing the surface energy lowers. Therefore, even if such a skin layer is provided, it is impossible to sufficiently keep the effect all through the service life of the photoreceptor drum.